The translation of the messenger RNA (mRNA) for rat growth hormone (GH) in a cell-free system derived from mouse ascites has recently been demonstrated. The availability of such a system for the detection of GH mRNA will form the basis for a number of projects. 1. GH mRNA will be identified in and isolated from a line of rat pituitary tumor cells (GC). Techniques involving either immune precipitation of GH-specific polysomes or fractionaction of mRNA on the basis of size will be employed to isolate GH mRNA. 2. The properties of the product of the in vitro translation of GH mRNA will be compared to those of GH synthesized in vivo by the GC cells. GH mRNA levels in a variant cell line which does not produce GH (GH4) will be determined. The effect on GH mRNA levels of factors which affect the synthesis of GH will be determined. 3. When purified GH mRNA is available, it will be used as a template for the synthesis of radioactive complementary DNA (cDNA). This cDNA will be used in studies of the multiplicity of the genes for GH, and of the state of GH mRNA in the nucleus of the GC cells.